Human parvovirus B19 is the only member of the Parvoviridae family known to cause diseases in humans. Parvovirus B19 infection causes fifth disease in children, polyarthropathy syndromes in adults, transient aplastic crisis in patients with underlying chronic hemolytic anemia, and chronic anemia due to persistent infection in immunocompromised patients. Hydrops fetalis and fetal death have been reported after maternal infection with parvovirus B19 during pregnancy (Brown et al., 1994, Crit. Rev.Oncol./Hematol. 16:1-13).
Parvovirus B19 exhibits a selective tropism for erythroid progenitor cells. The virus can be cultured in erythroid progenitor cells from bone marrow, fetal liver cells, and cell lines such as UT7/Epo or KU812Ep6. (Ozawa et al., 1986, Science 233:883-886; Brown et al., 1991, J. Gen. Vir.72:741-745; Komatsu et al., 1993, Blood 82:456-464; Shimomura et al., 1992, Blood 79:18-24; Miyagawa et al., 1999, J. Virol. Methods 83:45-54). Although the virus can be cultured in these cells very little virus is produced. The selective tropism of the virus is mediated in part by neutral glycolipid globoside (blood group P antigen), which is present on cells of the erythroid lineage (Brown et al., 1993, Science, 262:114-117). The presence of globoside on the surface of a cell is a determinant of viral tropism. Parvovirus B19 has a cytotoxic effect on erythroid progenitor cells in bone barrow and causes interruption of erythrocyte production. Human bone marrow cells that lack globoside on the cell surface are resistant to parvovirus B19 infection (Brown et al., 1994, N. Engl. J. Med., 33:1192-1196).
The ends of the parvovirus B19 genome have long inverted repeats (ITR), which are imperfect palindromes that form double-stranded hairpins. The role of the ITRs in the parvovirus B19 viral life cycle is unknown due to the inability to produce an infectious clone containing complete ITR sequences. In other parvoviruses, ITRs play an important role in the viral life cycle: they serve as primers for the synthesis of the complementary strand of viral DNA and are essential for the replication, transcription, and packaging of virus DNA (Bems, K (1990) in Virology, eds. Fields et al. Raven Press Ltd, NY, ppl743-1763). Previous attempts to produce an infectious clone of parvovirus B19 were unsuccessful due to deletions in the ITR sequences and the instability of the ITRs in bacterial cells (Deiss et al., 1990, Virology 175:247-254; Shade et al., 1986, J. Virol. 58:921-936). Methods of consistently producing infectious B19 parvovirus in cell culture are not known.
Thus, there remains a need to develop an infectious clone of parvovirus B19. A B19 infectious clone and methods of producing B19 infectious clones can be useful for producing infectious virus. Infectious virus is useful for identifying and developing therapeutically effective compositions for treatment and/or prevention of human parvovirus B19 infections, such as for example, antibodies, attenuated vaccines, and chimeric viral capsid proteins comprising antigenic epitopes.